Integrated circuits are still raising the degree of integration; in the manufacture of semiconductor tips such as VLSI's, it has become essential to process ultra-fine patterns comprising line widths below a quarter micron. As one of the means to reduce pattern dimension, it is well known to make short the wavelength of the exposure energy source used for resist pattern formation.
As an example, in the manufacture of semiconductor tips having a degree of integration up to 64 Mbits, the i line (365 nm) of a high-pressure mercury lamp has been used as the exposure source. As positive resists for this light source, a number of compositions based on a novolac resin and naphthoquinonediazide as a photo-sensitive material have been developed, which have achieved satisfactory results in the processing of lines having widths up to about 0.3 μm. Further, in the manufacture of semiconductor tips having a degree of integration of 256 Mega bits or higher, the KrF excimer laser light (248 nm) instead of the i line has been adopted as the exposure light source.
Further, in order to cope with the manufacture of semiconductors with a degree of integration of 1 Giga bits or higher, the use of the ArF excimer laser light (193 nm) and, further for the formation of patterns not exceeding 0.1 μm size, the use of the F2 excimer laser light (157 nm) are under investigation.
To adapt themselves to the wavelength shortening in the light source, the ingredients composing resist materials and their chemical structures are also changing drastically. Since the conventional resist comprising a novolac resin and a naphthoquinonediazide compound exhibits a strong absorption in the deep UV region around 248 nm, the light is difficult to reach the bottom portion of the resist, thus the resist being of low sensitivity and giving patterns having a tapered configuration.
To solve such problems, the so-called chemical amplification resists have been developed in which a resin having a fundamental backbone of poly(hydroxystyrene) that exhibits a weak absorption in the 248 nm region and is protected by an acid-decomposable group is used as a principal ingredient, and in which a compound (photo acid generator) that generates an acid upon irradiation with a deep UV light is jointly used. The chemical amplification resist, which changes the solubility in the developer via a decomposition reaction catalyzed by the acid generated at exposed areas, can form high-resolution patterns with a small amount of exposure.
However, in the case of using an ArF excimer laser light (193 nm), a satisfactory performance was not achieved even with the chemical amplification resist since compounds having an aromatic group essentially exhibit a strong absorption at the 193 nm wavelength region.
To solve this problem, an improvement of chemical amplification resists is being investigated by replacing the acid-decomposable resin having a fundamental backbone of poly(hydroxystyrene) to another acid-decomposable resin in which an alicyclic structure not absorbing 193 nm light is introduced in the main or side chain of a polymer.
For the F2 excimer laser light (157 nm), however, even the above-cited alicyclic resins proved to have a strong absorption in the 157 nm region, thus being unsatisfactory to form 0.1 μm or finer patterns. In contrast, it has been reported in Proc. SPIE, Vol. 3678, p. 13 (1999) that resins to which fluorine atoms are introduced in the form of perfluoro structure exhibit a sufficient transparency for the 157 nm radiation. Further, effective structures of such fluorine-containing resins have been proposed in Proc. SPIE, Vol. 3999, p. 330 (2000), p. 357 (2000) and p. 365 (2000), WO-00/17712, etc.
At SPIE's Micro-lithography Symposium 2001, a resist for the F2 light using a copolymer of 4-[bis(trifluoromethyl)-hydroxymethyl]styrene with t-butyl methacrylate was reported. But the resist based on this copolymer had a problem that the roughness of the pattern surface after development is too large. Moreover, the number of particles in the resist fluid was large, which further increased with the expansion of storage period thus causing a problem in storage stability.
In addition to these problems, there was still another problem that a large amount of scum generated in the space portions in line-and-space patterns. In the specification of DE10054996A is disclosed a resin for F2 resists obtained by copolymerizing an acrylate monomer having a fluorine atom at the α-position or in the ester moiety with p-hydroxystyrene or a tertiary ester-containing (meth)acrylate. However, this type of resist also suffered from the problem of noticeable scum generation in the space portion in line-and-space patterns.
Resists containing these fluoro-resins exhibited an insufficient dissolution contrast between the exposed and unexposed regions. Further, due to the specific water-repellent as well as oil-repellent property originating from the perfluoro structure, the improvement of the coating performance (the uniformity of the coating surface) and the suppression of development defect were also expected.